The phenomenon of stable quantum differences in permeability of the guts of voles to virulent Francisella tularensis is being studied further. We have found that the permeability does not depend on virulence of the ingested organism because the gut is also permeable to the much attenuated live vaccine strain (LVS) organisms as well when they are given in sufficient numbers and concentration. We are testing voles to determine whether the differences in gut permeability extend to other unrelated sustances (e.g., botulinum toxin). If the mechanism of resistance of some members of the population can be identified and it can be manipulated or stimulated, it may be possible to reduce susceptibility to enteric pathogens and to reduce gram-negative bacteriuria of importance, especially in infants. The mechanism by which a virulent and acutely lethal organism (when given parenterally) causes chronic infection when given by the enteral route is also under study.